1. Field of the Invention
The present invention concerns friction clutches, notably for motor vehicles, and relates more particularly to the unitary assembly which such a clutch has, described for example in the documents FRY-A-2 242 892 and FRY-A-2 420 690. Such a unitary assembly is referred to as a clutch mechanism.
2. Description of the Related Art
Conventionally, a friction clutch has a driving flywheel, possibly in two parts in order to form in particular a torsion damming flywheel or a flexible flywheel. The driving flywheel has a reaction plate.
The driving flywheel is fixed with respect to rotation to a first shaft, such as a driving shaft, namely the crankshaft of the internal combustion engine in the context of an application to a motor vehicle.
The reaction plate has a friction face on the back and is fixed with respect to rotation to a pressure plate able to move axially with respect to the reaction plate.
This pressure plate has on the front a friction face opposite that of the reaction plate.
The friction linings of a friction disc are interposed between the pressure and reaction plates, or more precisely between the friction faces thereof, forming friction tracks.
These linings are fixed to a support, usually elastically deformable axially in order to form a progressive friction disc affording assistance during the declutching operation. This support, possibly duplicated, is rigidly or elastically connected to a hub fixed with respect to rotation to a second shaft, such as a driven shaft, namely the input shaft of a movement transmission, for example a gearbox, in the context of an application to a motor vehicle. As a variant, the support is embedded in a friction lining. In all cases, the friction disc has at its external periphery two friction faces which wear during the service life of the clutch.
When the friction lining or linings are clamped between the pressure and reaction plates (clutch engaged), the torque is transmitted from the driving shaft to the driven shaft via the friction disc. When the friction linings are not clamped between the said plates (clutch disengaged), the driven shaft is not driven by the driving shaft. To do this, axially acting engagement means are provided and form an assembly with disengagement means designed to counteract as required the action of the engagement means bearing on a cover for action on the pressure plate, or more precisely for action on support means carried by the pressure plate fixed with respect to rotation to the cover whilst being able to move axially with respect to the latter, for example by means of a connection with axially elastic tongues or by means of a connection of the mortice and tenon type; radial lugsxe2x80x94forming tenonsxe2x80x94on the pressure plate being engaged for axial sliding in groovesxe2x80x94forming morticesxe2x80x94in the cover.
This cover has at its external periphery fixing means for fixing it to the reaction plate detachably or non-detachably.
The engagement means include at least one Belleville washer and the disengagement means of the disengagement levers for action on the disengagement means. Usually these engagement and disengagement means belong to the same axially elastic piece referred to as the diaphragm. This diaphragm, frustoconical in shape in the free state, has a peripheral part in the form of a Belleville washer, extended radially towards the centre by a central part divided into radial fingers by blind slots with broadened bottoms to form broadened orifices at the internal periphery of the Belleville washer constituting the axially acting engagement means, whilst the radial fingers form disengagement levers and therefore the clutch disengagement means.
In the documents FRY-A-2 242 892 and FRY-A-2 420 690, the cover constitutes, with the pressure plate, the elastic tongues and the diaphragm, a unitary assembly called a clutch mechanism, which is attached to the reaction plate. Naturally this clutch mechanism can constitute, with the friction disc and reaction plate, a module which is attached in a unitary fashion to the crankshaft of the vehicle engine or to a flange fixed to the crankshaft, the reaction plate then being fixed to the flange, advantageously flexible.
This mechanism is advantageously equipped with a compensation device, referred to as a wear take-up device, in order to compensate for the wear on the friction lining or linings and the friction faces of the pressure and reaction plates so that the diaphragm has a substantially constant position when the clutch is engaged, and this throughout the service life of the friction clutch. The diaphragm thus exerts a substantially constant load on the pressure plate in the clutch-engaged position. The travel of the clutch release bearing, acting on the internal end of the fingers of the diaphragm, is, in a known manner, substantially constant during the disengagement operation.
This wear take-up device has ramps and counter-ramps acting between the pressure plate and the support means of the diaphragm or between the diaphragm and the cover.
A trigger, sensitive to the state of wear on the friction lining or linings, makes it possible to make the ramps turn in the event of wear so that the diaphragm always occupies the same position when the clutch is engaged under the action of the engagement means (linings clamped).
The trigger has, in one embodiment, a ratchet wheel and a worm system, forming part of a cartridge as described in the document FR-A-2 753 503.
More precisely, an elastic member is provided with a control tongue cooperating with the teeth on the ratchet wheel and a non-return catch.
In the event of wear, the control tongue is maneuvered by an actuator, in this case an appendage of the diaphragm, in order to cause the ratchet wheel to turn and compress a take-up spring allowed subsequently to expand. A non-return catch prevents the worm from turning in the opposite direction, notably when the spring expands. The worm comes into engagement with the set of teeth integral with a ring provided with ramps for cooperating with counter-ramps fixed to the pressure plate.
Thus, in the event of wear, the thickness of the pressure plate, composed of the pressure plate proper and the ring with ramps, is increased, the said ring carrying support protrusions constituting the support means for the engagement means.
The ring therefore comes into engagement directly with the worm.
Such an arrangement gives satisfaction, but nevertheless the applicant has wondered whether it is not possible to eliminate the non-return catch in order to simplify the elastic member.
According to the invention, an engagement mechanism of the above indicated type is characterised in that the set of teeth belong to an intermediate piece connected with respect to rotation to the ring with ramps by means of connecting with respect to rotation allowing an axial movement of the ring with ramps with respect to the intermediate piece.
By virtue of the invention, the non-return catch can be omitted because the set of teeth is solely coupled in rotation to the ring with ramps by the intermediate piece and because the worm can drive the set of teeth in rotation but not vice-versa, the connection being of an irreversible design. Because the set of teeth is not axially connected to the ring with ramps and is therefore not driven by the latter during engagement and disengagement operations, the connection between worm and set of teeth can be reversible. The intermediate piece is axially fixed overall and consists for example of a washer. By virtue of the invention, the presence of a ratchet wheel and control tongue is no longer obligatory. This is because the appendage on the diaphragm can enter a recess in a drum as described in the document FR-A-2 424 442.
In one embodiment, the connection is of the cooperation of shapes type with circumferential mounting clearance and the elastic tongues rotatably connecting the pressure plate to the cover are used for gripping a washer, constituting the intermediate piece, between two tongues in the same set of tongues. To do this, the tongues have protuberances for gripping the intermediate washer. In one embodiment, the protuberances are produced at the end fixing the tongues to the cover. The intermediate washer is thus axially fixed and is provided for example with scallops into which there enter lugs on the ring with ramps thus connected with respect to rotation, with axial mobility, to the intermediate washer by cooperation of shapes.
Naturally, the structures can be reversed, the washer having radial lugs entering into axial scallops in the ring with ramps. As a variant, the intermediate piece is elastically coupled with respect to rotation to the ring with ramps, for example by means of at least one coil spring replacing the take-up spring abutting the worm.
As a variant, the intermediate piece with set of teeth is connected with respect to rotation to the ring with ramps by second axially elastically deformable tongues of the type, referred to as first tongues, acting between the pressure plate and the cover. In this way the friction between the ring with ramps and the intermediate piece is eliminated, the second tongues, in an embodiment with tangential orientation, being coupled at one of their ends to the ring with ramps and at their other end to the intermediate piece carrying the set of teeth.
By virtue of the second tongues, the losses of material can be reduced, the intermediate piece and the ring with ramps being able to be made from the same metallic blank by cropping, the intermediate piece surrounding the ring with ramps.
It should be noted that the second axially elastic tongues in all cases allow the formation of a sub-assembly consisting of intermediate piece and ring with ramps, which can be manipulated and transported. This facilitates the final assembly.
In addition, these second tongues are advantageously mounted with prestressing and exert a return action on the intermediate piece in the direction of at least one stop carried by the cover because of the fact that the ring with ramps is, by means of its support means, in contact with the diaphragm, or more precisely with the external periphery thereof. Thus, because of the prestressing of the second tongues, the sub-assembly consisting of ring with ramps, second tongues and intermediate piece has a thickness in the free state greater than that which it has when it is mounted in the clutchxe2x80x94with clutch engaged between the stop and the diaphragm. The prestressing is advantageously chosen so that the aforementioned sub-assembly is always in contact with the diaphragm and the stop when the clutch is disengaged. The second tongues are arched in order, in a second embodiment, to effect the prestressing. They can have a curved shape. This stop can be formed by means of protuberances belonging to the first tongues. The stop can be divided or continuous. In a variant, the stop is formed by means of rigid pieces serving to grip the first tongues between them and an area of a radial edge which the cover has at its external periphery. Thus the first tongues are protected and they are used to lock the stop or stops with respect to rotation by cooperation of shapes.
By way of variant, the stop is formed by means of balancing masses for the clutch mechanism made necessary by the presence of a cartridge including the worm carried by the cover.
This cartridge is mounted in a housing which the cover has for this purpose. The cover in reality has more than one housing. The empty housings are used for mounting balancing masses serving as a stop for axially locking, in one direction, the intermediate piece which thus has no need to be gripped since it is immobilised axially in the other direction by the ring with ramps in contact with the diaphragm under the return action exerted in the second tongues for connection in rotation with the ring with ramps.
These second tongues can be tongues of the standard type, that is to say of the same type as the first tongues. By virtue of these tongues, the intermediate piece can be centred with respect to a skirt on the cover so that the pressure plate has no need to be machined in order to centre the ring with ramps and so that the ring with ramps is simplified since it is no longer necessary to provide a centring edge on it.
The presence of the intermediate piece makes it possible to locate at least one take-up spring between the intermediate piece and the ring with ramps, which simplifies the cartridge carrying the worm.
The intermediate piece can be not in the form of a continuous ring, particularly when it is connected by tongues to the ring with ramps.
These second tongues can have another shape, for example a concertina shape. The second tongues can also have a circumferential action and thus constitute a take-up spring. To do this, they advantageously have a concertina shape, which makes it possible to eliminate the take-up spring at the level of the cartridge, the tongue being mounted with prestressing between the ring with ramps and the intermediate piece.
As a variant the second tongues, instead of being arched, are flat originally and it is the first tongues, whose return force is then increased, which force the intermediate piece in the direction of the ring with ramps.
Removable hooks or links, for example in the form of clips, act, in one embodiment, between the intermediate piece and the ring with ramps in order to protect the second tongues before mounting the aforementioned sub-assembly thus created on the cover. As a variant the hooks can be replaced with screws, bolts, etc, which are removed finally in the same way as the hooks. In all cases the intermediate piece is pressed against an axial stop carried by the cover and designed to maintain the intermediate piece in the axial direction going from the cover to the pressure plate. In one embodiment the take-up spring is mounted under prestressing so that the take-up takes place principally during re-engagement and the wear and relative movements between the set of teeth and the screw are reduced.